496 Bashford Dean Memorial Volume 



TABLE IV. 

 PALINGENETIC CHARACTERS OF CHLAMTDOSELACHUS 

 Teeth, of "cladodont" type, are formed by the fusion of simple denticles. 

 At the angles of the mouth, scales grade into teeth. 

 The notochord persists with very little constriction. 

 Calcification of the endoskeleton is very limited in amount. 

 Cyclospondylous vertebral centra are incipient or rudimentary. 

 The visceral skeleton shows a striking gradation between jaws and gill-arches. 

 Nearly complete series of basibranchials and hypobranchials, with little fusion. 

 In the trunk musculature, longitudinal divisions are few and simple. 

 The digestive tube is relatively simple and is nearly straight. 

 The bursa entiana is not invaded by the spiral intestine. 

 In the valvular intestine, the apices of the anterior and posterior coils point in different directions. 



In the middle portion of the spiral intestine, there is an axial strand; in both anterior and posterior portions, 

 there is an axial tube. 



The liver is bilaterally symmetrical. 



In some specimens, there is a persistent thyroglossal duct lined with pharyngeal mucosa. 



Pouch-like vestige of the ventral end of the spiracular gill cleft. 



In the female, the mesonephroi persist through almost the entire length of the body cavity. 



In females, there is a pair of urinary sinuses which open separately into the urogenital smus. 



In females, nearly all the collecting tubules enter the mesonephric duct. So-called ureters are absent. 



Epibranchial (efferent branchial) arteries are situated dorsal to the respective gill-arches, as in the embryos 

 of other sharks. 



Posterior efferent collector arteries may retain a dorsal connection with the anterior efferent collector of the 

 same gill. 



The brain is very small; the forebrain is small proportionally. 



The roof of the definitive forebrain is said to be non-nervous. 



In a 25-mm. embryo, the glossopharyngeal nerve has a ventral root. 



The "nervus collector" is unusually well developed. 



The lateral line sensory canal is an open groove from the tip of the tail as far forward as the spiracle. Several 

 of the longer sensory canals of the head are open. 



Whether open or closed, the sensory canals of the lateral line system are cutaneous rather than subcutaneous. 



The gular division of the sensory canal system corresponds to the "gular line" of pit organs in Heptanchus, 

 Squalus and Mustelus, 



